The present invention relates to polyvinylidene fluoride resin compositions, and more particularly to polyvinylidene fluoride resin compositions which can be suitably used in the fields of which semiconductivity and/or transparency are required.
The resin compositions according to the present invention are suitable for use, for example, as resin materials for forming at least surface layers of charge controlling members (semiconductive members) such as charging rolls, transfer rolls, image-forming rolls, charging belts and destaticizing belts in image forming apparatus of the electrophotographic system making good use of their semiconductivity. The resin compositions according to the present invention are also suitable for use in application fields making good use of their static electricity controlling property, antistatic property, anti-dust-collecting property and the like, for example, as charge controlling members such as packaging materials (for example, films, bags and containers) for electronic parts, wall paper, sheathing materials for OA apparatus and anti-static partitions. In the present invention, the term, xe2x80x9csemiconductive resin compositionxe2x80x9d means a resin material the volume resistivity of which lies between an insulator and a metallic conductor, and more specifically means a resin material having a volume resistivity of about 105-1013 xcexa9cm.
The resin compositions according to the present invention are suitably used, as application fields making good use of transparency (high light transmittance and low haze), as optical resin materials for optical members such as optical fibers and lenses, light-transmitting materials for solar cells, and lightening covers. The resin compositions according to the present invention are suitably used as optical members such as anti-dust-collecting window glass and protective materials for displays making good use of both properties of semiconductivity and transparency.
In the fields of electric and electronic apparatus, resin materials the volume resistivities of which have been precisely controlled are demanded as semiconductive materials. For example, in image forming apparatus (electrophotographic copying machine, electrostatic recording apparatus, etc.) of the electrophotographic system, such as copying machines, facsimiles and laser-beam printers, images are formed through steps such as charging, exposure, development, transfer, fixing and static charge eliminating. In order to form respective members used in these steps, resin materials the volume resistivities of which have been precisely controlled are required.
A charging roll or belt, a transfer roll or belt, a developing roll, a blade for controlling the thickness of a toner layer, and the like installed in such an image forming apparatus are required to be semiconductive at least at their surface layers, and specifically to have a desired volume resistivity within a range of about 105-1013 xcexa9cm. For example, in a charging system making use of the charging roll or belt, voltage is applied to the charging roll or belt, and the charging roll or belt is then brought into contact with a photosensitive drum, whereby an electric charge is directly applied to the photosensitive drum to equally and uniformly charge the photosensitive drum. In a development system making use of the developing roll, a toner is adsorbed in a charged state on the surface of the developing roll by frictional force between the developing roll and a toner supply roll, and this toner is uniformly leveled by the blade for controlling the layer thickness of the toner, and the toner is then caused to fly toward an electrostatic latent image formed on the photosensitive drum by electric attraction force to develop the latent image. In a transferring system making use of the transfer roll or belt, voltage having a polarity opposite to that of the toner is applied to the transfer roll or belt to generate an electric field, whereby the toner on the photosensitive drum is transferred to a transfer material by electric attraction force generated by the electric field.
Accordingly, the charge controlling members such as the charging roll or belt in the image forming apparatus are required to have a low volume resistivity within a proper range. The volume resistivity itself is required to be uniform in distribution. If the volume resistivity varies with location, no high-quality image can be provided. For example, if the volume resistivity distribution of the charging roll or belt is uneven, it is difficult to equally and uniformly charge the photosensitive drum, so that the quality of the resulting image is deteriorated. In these members, it is also required that their volume resistivities and surface resistivities are not very changed by change of humidity. If the volume resistivities and surface resistivities of the charge controlling members are greatly changed by change of humidity in an ordinary use environment, no high-quality image can be stably provided.
Further, when dust, toner and/or the like are adsorbed on sheathing materials and parts of OA apparatus formed from a resin material, their appearances are impaired, or the cause of trouble is formed. When resin-made apparatus and parts used in the fabrication processes of semiconductor devices, LCD and the like, and films, bags and containers for packaging electronic parts such as IC and LSI adsorb dust by generation of static electricity, the quality of the electronic parts is impaired. It is therefore required that a volume resistivity of about 1051013 xcexa9cm is imparted to resin materials used in these application fields, particularly, in face-layer materials thereof so that they may have good charge controlling.
As methods for lowering the electrical resistance (volume resistivity) of polyvinylidene fluoride resins and molded or formed products (hereinafter may be referred to as xe2x80x9cmoldingsxe2x80x9d) thereof, there have heretofore been known (1) a method in which an organic antistatic agent is applied to the surfaces.of the resin moldings, (2) a method in which an organic antistatic agent is incorporated into the resins, (3) a method in which a conductive filler such as carbon black or metallic powder is incorporated into the resins, and (4) a method in which an ionic electrolyte is incorporated into the resins.
However, the method (1) involves a problem that since the polyvinylidene fluoride resins have excellent anti-adhesion property, the antistatic agent easily falls off from the surfaces of the moldings by wiping or washing the surfaces. In the method (2), a surfactant or hydrophilic resin is used as the organic antistatic agent. Since the method making use of the surfactant adopts a mechanism that the surfactant is caused to bleed out of the surface of each molding, thereby imparting antistatic property thereto, its volume resistivity and antistatic property are greatly changed by changes of environments such as temperature and humidity. In addition, high stain resistance, which is a merit of the polyvinylidene fluoride resins, is impaired. In the method making use of the hydrophilic resin, it is necessary to incorporate a great amount of the hydrophilic resin in order to achieve a desired antistatic effect. Therefore, excellent physical properties inherent in the polyvinylidene fluoride resins, such as stain resistance, weather resistance, ozone resistance and solvent resistance, are lowered. In addition, the method involves a problem that the dependency of volume resistivity and antistatic property on humidity becomes high. The stain resistance and solvent resistance are properties required in the case where a toner applied to a member arranged in an image forming apparatus of the electrophotographic system is removed by cleaning. Since an image forming apparatus equipped with a corona discharge device or the like generates ozone, the ozone resistance is also a property required of members in such an apparatus. The weather resistance is a property required in the case where the resins are used as surface-protecting materials for outdoor sign boards and window glass.
The method (3) is adopted in many fields. For example, a charging roll is formed by coating a core bar with a semiconductive resin composition obtained by incorporating a conductive filler into a resin. However, the semiconductive resin composition with the conductive filler dispersed in the resin generally has an extremely uneven distribution in volume resistivity. In mane cases, a scatter of the distribution amounts to several figures. Therefore, such a semiconductive resin composition has involved a problem from the viewpoint of practical performance. In particular, the polyvinylidene fluoride resin is small in surface energy, and has hence involved a problem that when a conductive filler is dispersed therein, the conductive filler becomes migrated in the resin by the application of high voltage, or the like, so that its volume resistivity varies. In addition, the polyvinylidene fluoride resin composition with the conductive filler dispersed therein is generally insufficient in dielectric strength and is not always suitable for use in application fields to which high voltage is applied repeatedly. Further, the charged amount of the conductive filler must be increased in order to attain the required level of semiconductivity. For that reason, there is encountered a problem that the molding and processing ability and mechanical strength of the resulting polyvinylidene fluoride resin composition are lowered, or its hardness becomes too high. Further, the polyvinylidene fluoride resin composition with the conductive filler dispersed therein is often colored by the conductive filler such as conductive carbon black. Therefore, such a composition is unsuitable for use in application fields such as sheathing materials for OA apparatus and wall paper.
The method (4) of incorporating the ionic electrolyte is expected to be a method effective for imparting semiconductivity to a polyvinylidene fluoride resin, judging from the fact that polyvinylidene fluoride (PVDF) has been known from of old to be a good conductor to ions (for example, Japanese Patent Application Laid-Open Nos. 32330/1976, 110658/1976, 111337/1976 and 127872/1979). However, a resin composition obtained by incorporating an inorganic metal salt such as lithium chloride or potassium chloride, which is a typical electrolyte, into a polyvinylidene fluoride resin has been difficult to lower its volume resistivity to 1xc3x971013 xcexa9cm or lower, since these inorganic metal salts are only slightly soluble in the resin. There has also been a problem that the aggregate of the inorganic metal salt added in excess forms the cause of fish eye. When kneading is conducted at a higher temperature or for a longer period of time in order to dissolve the aggregate in the polyvinylidene fluoride resin, the resin and/or the electrolyte is decomposed to impair its substantial mechanical properties and appearance. In the case of a deliquescent metal salt such as a Li salt, the resulting resin composition becomes hygroscopic when it is filled in a great amount. Therefore, this case involves problems that the volume resistivity of the composition is greatly changed by change of humidity, and that the surface of the resulting molding becomes sticky due to the deliquescence of the metal salt bled out.
As a method for improving the solubility of the electrolytes in a resin, Japanese Patent Application Laid-Open Nos. 177064/1985 and 72061/1986 have proposed a method in which a polar solvent such as propylene carbonate is contained in the resin. However, this method has involved problems that the Young""s modulus of the resin is markedly lowered, and that the surface of the resin becomes sticky due to the electrolyte and solvent bled out.
There have hitherto been proposed methods of using a quaternary ammonium salt as an antistatic agent for resins. For example, Japanese Patent Publication No. 26973/1980 discloses an antistatic coating material with a quaternary ammonium salt and a resin dissolved in an organic solvent. However, this coating material is easy to fall off by washing and is hence difficult to retain its antistatic effect for a long period of time. Japanese Patent Application Laid-Open No. 3835/1972 discloses an antistatic sheet with a quaternary ammonium salt incorporated into polyolefin. However, this antistatic sheet depends on a mechanism that its antistatic effect is exhibited by bleeding of the quaternary ammonium salt out of the resin, so that its conductivity and antistatic effect are greatly changed by changes of environments such as temperature and humidity. In addition, since the electrolyte is hard to be ionized in a resin having.a low polarity, such as polyolefin, the volume resistivity of the resin cannot be lowered, though its surface resistivity can be lowered. Further, since most quaternary ammonium salts, particularly, quaternary. ammonium halides are poor in heat stability, disadvantages such as foaming and coloring arise in the resulting moldings when such a quaternary ammonium salt is melt-mixed with a polyvinylidene fluoride resin (the processing temperature of this resin is about 220 to 270xc2x0 C.).
Since many metal salts and quaternary ammonium salts are easy to bleed out in a high-humidity environment in particular, they have involved problems that metallic impurities on the surface of a static electricity-controlling packaging material form the cause of rejected products, for example, in a fabrication process of semiconductor devices, and that in a transfer roll or belt installed in an image forming apparatus of the electrophotographic system, its surface layer undergoes a change in volume resistivity due to the reduction of electrolytes in a resin, resulting in deterioration of image quality.
With respect to optical materials, in recent years, there has been a strong demand for development of transparent resin materials light and excellent in processability in the field of optoelectronics. However, transparent resin materials usable in the optical application fields have been limited to polymethyl methacrylate, polycarbonate, polystyrene, a part of polyolefin resins having an alicyclic structure, and the like. When such conventional resins are used for pickup lenses in, for example, compact disks and magneto-optical disks, a lens made of any one of the resins easy to absorb moisture, such as polymethyl methacrylate, polystyrene and polycarbonate, undergoes changes in dimensions and refractive index due to moisture absorption, which proceed from its surface, so that the properties of the lens become uneven as a whole. Therefore, such a lens has involved a problem that the wave surface of a laser beam is disordered by such unevenness to adversely affect both write and read. A pickup lens of a compact disc player installed in a car is required to have high heat resistance of 100 to 130xc2x0 C. or higher. However, polymethyl methacrylate has been difficult to satisfy such a requirement.
In general optical systems such as projection televisions and cameras, chromatic aberration caused by differences in focal length according to wavelengths of light occurs at all costs in the case where only one lens is used. Therefore, a design called xe2x80x9cachromatismxe2x80x9d, in which chromatic aberration is dissolved by combining a lurality of materials different in refractive index and Abbe""s number from each other, is required. In glass lenses, the achromatic design can be made with comparative ease because the number of glass different in refractive index and Abbe""s number amounts to at least 200 kinds. However, when only plastic lenses are used, the achromatic design is very difficult because usable transparent resin materials are only several kinds as described above, and the refractive indices of the respective resin materials concentrate on about 1.5 to 1.6. Therefore, novel transparent resin materials have been always demanded in this field.
As optical fibers, there have been known glass type optical fibers using fused quartz or compound glass as core and clad components and besides plastic optical fibers the core component and clad component of which are both formed from a plastic. The plastic optical fibers are easy in production and handling and cheap compared with the glass type optical fibers, and on the other hand, have had demerits that they are poorer in durability and heat resistance and greater in transmission loss.
Polyvinylidene fluoride (PVDF) is excellent in heat resistance and weather resistance, little in moisture absorption and as lower as about 1.42 in refractive index compared with other transparent resins, and is hence expected as.a clad component for plastic optical fibers. However, PVDF is easy to opacified by crystallization upon processing and forming or molding. Therefore, for example, Japanese Patent Application Laid-Open Nos. 22872/1988, 97901/1989, 60931/1993 and 106019/1996 have proposed a method in which PVDF is blended with an acrylic resin to make it transparent. However, such a method has had disadvantages that the excellent heat resistance, weather resistance and non-hygroscopicity characteristic of PVDF are lowered by blending with the acrylic resin, and its refractive index also comes close to that of the acrylic resin. Further, a blend system composed of resins alone involves problems of tending to become optically uneven and causing great light scattering.
Polyvinylidene fluoride resins are used as surface-protecting materials for office supplies, sign boards, building materials and the like making good use of their excellent weather resistance. However, they have been unsatisfactory in transparency to use as protective films for window glass and CRT.
As methods for improving the transparency of the polyvinylidene fluoride resins, there have heretofore been proposed a method in which an inorganic salt such as KCl or NaCl is used as a nucleating agent, and a method in which a substantially unstretched sheet-like or thread-like formed product is cold-stretched or stretched under high-temperature and high-pressure conditions. However, the method of adding the inorganic salt has involved a problem that the aggregate of the salt forms the cause of fish eye. The method of cold-stretching the substantially unstretched sheet-like or thread-like formed product or stretching it under high-temperature and high-pressure conditions requires a vast processing apparatus and has hence involved a problem from the viewpoint of productivity. In addition, both methods have been insufficient in the effect of improving the transparency.
It is an object of the present invention to provide a polyvinylidene fluoride resin composition which can stably and uniformly achieve a desired volume resistivity within a range of 105-1013 xcexa9cm with good precision, and undergoes little changes in volume resistivity and surface resistivity by change of environmental moisture.
Another object of the present invention is to provide a polyvinylidene fluoride resin composition having a high light transmittance, a low haze and excellent transparency.
A further object of the present invention is to provide various kinds of semiconductive and/or transparent formed or molded products such as tubes, sheets, fibers and injection-molded products using such a resin composition excellent in semiconductivity and/or transparency.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that a resin composition obtained by adding an alkyl quaternary ammonium sulfate or sulfite to a polyvinylidene fluoride resin in a specific proportion is excellent in transparency, has a volume resistivity within a semiconductive region, is free of a scatter of volume resistivity with location and can stably achieve the desired volume resistivity with good precision. This resin composition also neither forms any aggregate or fish eye nor undergoes the bleeding of any additives. Further, the resin composition has good processability and can hence be formed into various formed or molded products by conventional melt processing techniques. The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a polyvinylidene fluoride resin composition comprising 100 parts by weight of a polyvinylidene fluoride resin (A), and 0.03 to 10 parts by weight of at least one compound (B) selected from the group consisting of alkyl quaternary ammonium sulfates (B1) represented by the formula (1): 
wherein R1 to R4 are alkyl groups which are the same or different from one another, and R5 is an alkyl or fluoroalkyl group or a hydrogen atom, and alkyl quaternary ammonium sulfites (B2) represented by the formula (2): 
wherein R6 to R9 are alkyl groups which are the same or different from one another, and R10 is an alkyl or fluoroalkyl group or a hydrogen atom.